Pre-emptive channel borrowing and traffic overflowing channel allocation scheme for multimedia overlay networks

This paper proposes a channel allocation scheme for multimedia wireless networks, in which a twolayer macro-cell or micro-cell architecture is considered. Macro-cells are used to access high-mobility services; while micro-cells, which are overlaid by the macro-cells, are used to cater low-mobility services. To analyze the scheme, a multidimensional Markov traffic model is firstly developed, in which traffic characteristic of two special periods of time is considered. And then, a pre-emptive channel-borrowing scheme combined with trafficoverflowing strategy for multimedia (voice, video or data) networks is proposed, in which handoff requests can not only borrow channels from adjacent homogenous cells, but also be overflowed to heterogeneous cells. Priority strategies are also dedicated to high-mobility services for they can pre-empt channels being used by low-mobility services in macro-cells. To meet the high quality of service (QoS) requirements of video services and increase the channel utilization ratio, video services can be transformed between real-time services and non-real-time services as necessary. Simulation results show that our schemes can decrease the blocking probabilities and improve the channel utilization.     

A new channel allocation scheme for hierarchical wireless networks

A channel allocation scheme for hierarchical wireless networks was proposed in terms of the connection-level quality of service. The channel allocation scheme was analyzed using both horizontal channel borrowing and vertical traffic overflowing. Pre-emptive priority strategies are used to classify real-time services and non-real-time services, real-time service is given higher priority for it is allowed to pre-empt channels used by non-real-time service. Some channel borrowing thresholds and acceptance ratios are used to avoid channel locking or dynamic power control, which can also be dynamically adjusted according to network load. Simula-tion results show that the proposed schemes can improve the system performance.     

A simulation study of service differentiation for the bandwidth request scheme in fixed IEEE 802.16 network

Various flexible mechanisms related to quality of service (QoS) provisioning have been specified for uplink traffic at the medium access control (MAC) layer in the IEEE 802.16 standards. Among the mechanisms, contention based bandwidth request scheme can be used to indicate bandwidth demands to the base station for the non-real-time polling and best-effort services. These two services are used for most applications with unknown traffic characteristics. Due to the diverse QoS requirements of those applications, service differentiation (SD) is anticipated over the contention based bandwidth request scheme. In this paper we investigate the SD with the bandwidth request scheme by means of assigning different channel access parameters and bandwidth allocation priorities at different packets arrival probability. The effectiveness of the differentiation schemes is evaluated by simulations. It is observed that the initial backoff window can be efficient in SD, and if combined with the bandwidth allocation priority, the SD performances will be better. Foundation item: the National Basic Research Program (973) of China (No. 2005C13321804)     

基于分组的宽带CDMA网络呼叫接纳控制方案

以宽带CDMA网络为研究对象，结合3种主要业务类型（话音、视频、数据）的精确建模，提出了用户连接接纳控制与用户分组接纳控制协作的CAC机制，以及基于优先级的改进CAC方案．该方案根据无线分组网络中以分组为最小资源管理单位的特点，结合系统剩余容量以及不同类型业务的特点，为不同业务设置不同的接入准则．优先接纳对实时性要求高的用户连接和分组，同时尽可能地保证实时性要求较低业务的服务质量．仿真结果表明，所提出的策略有效降低了业务接人的阻塞率和平均接纳延时，同时提高了系统资源利用率．     

AN OPTIMIZED SCHEME FOR FAST HANDOFF IN IP-BASED CDMA WIRELESS COMMUNICATION NETWORKS

IntroductionMobility as an essential characteristic of wire-less network has received considerable attention inrecent years.A number of system- specific solu-tions have been developed for2 G( such as GSM)and 3G( such as UMTS) wireles networks.Fromthe Internetpointofview these solutions can be re-garded as layer- 2 solutions for wireless access net-works working transparently to the layer- 3 ( IPlayer) [1] .The evolution of wireless network is be-ing strongly influenced by mainly two compo…     

用于云存储数据服务器的I/O请求调度算法

在云存储系统的体系架构中,当前对数据服务器守护进程的I/O请求调度采用先来先服务（first in first out）策略,这种调度策略没有考虑不同类型I/O请求的时效性要求,容易造成时效性要求高的I/O请求因被阻塞而无法得到及时处理,从而降低整个系统的服务质量.为解决该问题,本文提出一种用于云存储数据服务器的I/O请求调度算法.该算法首先对来自客户端的I/O请求进行分类,并赋予不同的优先级;然后以合适的时长作为周期、以分时间片的方式对不同优先级的I/O请求进行周期性的调度.分布式文件系统仿真实验结果表明,该算法在重负载情况下对实时请求的响应速度提高了20%,同时也兼顾了低优先级请求的响应性能.      

Dynamic Channel Allocation in Sectored Cellular Systems

It is known that dynamic channel assignment(DCA) strategy outperforms the fixed channel assignment(FCA) strategy in omni-directional antenna cellular systems. One of the most important methods used in DCA was channel borrowing. But with the emergence of cell sectorization and spatial division multiple access(SDMA) which are used to increase the capacity of cellular systems, the channel assignment faces a series of new problems. In this paper, a dynamic channel allocation scheme based on sectored cellular systems is proposed. By introducing intra-cell channel borrowing (borrowing channels from neighboring sectors) and inter-cell channel borrowing (borrowing channels from neighboring cells) methods, previous DCA strategies, including compact pattern based channel borrowing(CPCB) and greedy based dynamic channel assignment(GDCA) schemes proposed by the author, are improved significantly. The computer simulation shows that either intra-cell borrowing scheme or inter-cell borrowing scheme is efficient enough to uniform and non-uniform traffic service distributions.     

考虑匹配优先级的共享混合停车位租用与分配问题研究

为充分利用混合停车场的停车和充电资源，本文依据出行者需求的差异性设置匹配优先级，在此基础上以共享平台接受并出租车位的收益扣除拒绝请求的惩罚成本的总收益最大化为目标，以充电量不超过停车场负荷为约束条件，建立考虑匹配优先级的共享混合停车位租用与分 配(MPRA)模型。基于匹配优先级原则和模型特征改进蚁群算法，设置分块冲突矩阵，根据分块冲突矩阵设计蚂蚁信息素更新策略和路径选择策略并进行求解。最后算例证实了考虑匹配优先级的必要性，并分析了问题规模对MPRA分配方案的影响。研究结果表明：在充电需求匹配率方面，MPRA方案高于利润最大化方案，平均提升率为28.96%，这一优势与出行者数量或车位数量成反比，且利润提升率随着问题规模的增加而增加；车位数量有限时，MPRA方案相较于先到先停方案可以极大化提升车位利用率和充电需求匹配率，平均提升率分别为17.87%和113.96%。     

基于协整理论的短时交通流组合预测研究

交通流短时预测是智能交通系统中的一个重点问题,预测效果的好坏直接关系到控制和诱导的结果,是实现先进交通管理信息系统的关键技术之一. 本文简要介绍了协整和误差修正模型的概念,利用序列的协整性来进行交通流组合预测模型的有效性验证,并利用误差修正模型提高组合预测模型的稳定性. 我们利用北京市二环路上采集到的交通流数据进行了模型的验证. 研究结果表明,基于协整理论的交通流组合预测模型可以取得很好的预测效果.     

高速公路改扩建工程中交通分流方案研究

对不同车型的运行特性、施工干扰程度等因素进行分析,拟定分流优先级,利用组合试算法确定分流车型;通过分析不同层次交通的分布特性及对绕行距离的可接受程度,根据通道剩余承载能力和需分流交通量大小的关系,探讨如何确定交通分流方案,研究结论的得出可为高速公路改扩建交通分流方案设计提供理论依据。     

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本文提出了基于J2EE技术的城市交通诱导Web-GIS三层模型系统实现方案。并以北京市为例，采用Struts+ Hibernate+ JDBC技术构建了B/S结构的实时交通信息发布与诱导系统，克服了已有的城市交通信息Web-GIS系统只面向交通管理层的局限。该Web-GIS采用MapXtreme Java作为地图管理构建的瘦客户机/服务器模式，通过将查询道路与GPS实时浮动车数据进行动态匹配，来获得路线实时的交通信息，并结合重要的道路消息，为出行者提供可靠参考。     

非严格优先权下许可相位左转车辆侵占时距分布模型

提出侵占时距的概念来描述非严格优先权下许可相位左转车流的微观特性,并根据左转车辆通过时,交叉口内对向直行车辆的不同存在形式,划分成了4种交通状态.基于大量的实测数据,利用7种不同的模型对侵占时距分布进行拟合.采用最大似然估计法进行参数估计,通过Kolmogorov-Smirnov检验对不同模型在不同状态下的拟合优度进行判定.最终得到Log-Logistic模型对不同交通状态下的拟合效果最优,并且其模型参数值的大小与对向直行车辆的不同存在状态有关.最后,选取了2个交叉口作为验证组,验证了Log-Logistic模型在不同交叉口不同交通状态下的适用性.     

一种无线通信网中的跨层分组调度方案

提出了基于未来无线多媒体通信标准下的一种跨层分组调度方案,在调度时,首先对多媒体混合业务进行了合理分类,即实时性业务和非实时性业务;在调度优先级的确定过程中,利用跨层优化的思想估算优先级公式中的相关参数,由此给出了跨层分组调度方案的具体算法流程.仿真结果表明,与传统经典的比例公平调度算法（PFS）相比,该方案在实时性、数据吞吐量、信道利用率等方面具有更好的性能.     

Switching between antenna subset selection and quasi-orthogonal space-time block code in presence of correlation

We address the problem of adaptive modulation and coding scheme (AMCS) for a multi-input multioutput (MIMO) system in presence of time-varying transmitting correlation. Antenna subset selection and quasiorthogonal space-time block code (QOSTBC) have different error performances with different signal-to-noise ratios (SNRs) and in different spatial correlation scenarios. The error performance can be improved by selecting an appropriate transmission scheme to adapt to various channel conditions. The maximum distance criterion is the simplest and very effective algorithm for the antenna subset selection without needs of complex calculation and channel state information at transmitter (CSIT). The minimum error performance criteria and the simplified linear decision strategy are developed for constant transmission rate traffic to select the optimal transmission scheme. It can dramatically decrease algorithm complexity for obtaining error probability according to the known quantities comparing with using instant CSIT. Simulation results show that, remarkable performances including low SNR and weak spatial correlation at the expense of simple calculation and almost no bandwidth loss by adopting AMCS can be achieved. The proposed AMCS improves robustness of slowly varying spatial correlated channels.     

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宏观基本图（MFD）存在于具有交通运行同质性的城市路网中,它可以用于路网的服务水平评估、区域控制和宏观交通建模.不同道路运行条件对MFD的形状存在不同的影响,进行MFD影响因素分析是应用MFD理论研究城市交通运行规律的前提.本文以广州市海珠区为研究区域,运用Paramics交通仿真软件对海珠区的路网进行建模,通过采取不同交通管控措施,分析MFD图形的影响因素.结果表明,MFD不仅是路网本身的性质,也是控制策略效果好坏的直接体现.同时,需求的剧烈变化、公交专用道的设置、车道禁行都会不同程度的影响路网的MFD.另外,制定交通控制策略时要优先考虑路网中的关键路段.     

物理帧时槽交换中改进的DWRR调度算法

传统的DWRR(defic itwe ighted round rob in)调度算法不能满足变速率实时多媒体业务时延要求.为此,提出了改进的DWRR调度算法(improved DWRR).该算法在DWRR的轮询过程中插入1个新的服务优先等级,从而有效地保证变速率实时多媒体业务的时延要求,并且也可有效地调度非实时业务.仿真结果表明,对变速率多媒体实时业务,改进的DWRR算法的平均队列时延为3.4 m s,比传统DWRR算法的平均队列时延(4.9 m s)降低了30.6%.     

A Model of Federated Evidence Fusion for Real-time Urban Traffic State Estimation

In order to make full use of heterogeneous multi-sensor data to serve urban intelligent transportation systems, a real-time urban traffic state fusion model was proposed, named federated evidence fusion model. The model improves conventional D-S evidence theory in temporal domain, such that it can satisfy the requirement of real-time processing and utilize traffic detection information more efficaciously. The model frame and computational procedures are given. In addition, a generalized reliability weight matrix of evidence is also presented to increase the accuracy of estimation. After that, a simulation test is presented to explain the advantage of the proposed method in comparison with conventional D-S evidence theory. Besides, the validity of the model is proven by the use of the data of loop detectors and GPS probe vehicles collected from an urban link in Shanghai. Results of the experiment show that the proposed approach can well embody and track traffic state at character level in real-time conditions.     

基于交叉口重要度深度搜索的区域信号协调控制方法

城市路网规模的不断扩大,给城市交通控制系统带来严峻的挑战.本文对交叉口之间的交通关联关系及表征交叉口关联性的交通流参数进行了分析,从而明确路网的拓扑结构,建立了以路网拓扑结构为基础的交叉口重要度估计模型,并根据有向深度搜索算法设计了区域信号协调优化方法.该方法从全局的角度建立了一种均衡疏导路网交通流的信号协调控制方法.最后将本文提出的方法与Synchro7优化出的控制方案对比,利用微观仿真软件SUMO进行控制效益评价,仿真结果表明,本文的方法可以有效提高信号控制效益.     

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ETC技术的广泛使用有效提高了人工收费效率,缓解了收费站车流拥堵状况,本文对ETC系统优化配置方案进行了研究.根据收费站设计规范和实地调研成果,对高速公路收费站系统构件进行了形式化描述,结合系统各个构件中车辆的行为特征、车辆及收费通道的分类特征,建立了一种适用于高速公路ETC收费站系统的元胞自动机交通流模型.考虑到ETC收费站车流拥堵特性,提出了ETC收费站服务水平的概念及相关计算方法,设计以ETC使用率、ETC车道数量及交通流量为参数的仿真方案,选取封闭式4车道收费站进行仿真分析,基于仿真结果提出了ETC使用率分别为30%、60%和90%时ETC车道数的配置建议,为收费站管理人员合理利用ETC系统提供了理论依据.     

基于期望车速的跟驰模型研究

期望车速是驾驶员驾车过程中依据道路条件、车流状况、所驾驶车辆性能等因素,经综合考虑后存在于自身心目中并认为可以实现的一种＂目标车速＂,它对行驶车辆的实际行车速度高低产生影响。为了反映车辆运行过程中不同驾驶员运行车速选择的差异,本文提出了基于期望车速的跟驰模型。该模型能够解释不同驾驶员在相同道路条件下选择不同行车速度的原因。在建立模型的基础之上,作者讨论了保持交通流稳定性的充分和必要条件。最后,文中给出了应用实例。结果表明：当驾驶员的期望车速接近均衡车速时,交通流是稳定的;反之,当驾驶员期望车速与均衡车速差异较大时,交通流的稳定性可能下降。